Valmiki Ramayana Ayodhya Kanda Sarga 28 Shloka 19
Original Shlokaसरीसृपाश्च बहवो बहुरूपाश्च भामिनि। चरन्ति पृथिवीं दर्पात्ततो दुःखतरं वनम्।।2.28.19।।
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भामिनि O Beautiful lady, बहुरूपाः च of various forms too, बहवः many, सरीसृपाः च reptiles also, दर्पात् fiercely, पृथिवीम् on the ground, चरन्ति move about, ततः therefore, वनम् to live in the forest, दुःखतरं is extremely dangerous.
There are various forms of fierce reptiles fearlessly crawling on the ground. So (living in the) forest is extremely dangerous.